Σ^{+} and Σ[over ¯]^{-} Polarization in the J/ψ and ψ(3686) Decays

Area of Science:

• Particle Physics
• High Energy Physics
• Quantum Chromodynamics

Background:

• The study of hyperon decays provides crucial insights into fundamental symmetries in particle physics.
• Understanding spin polarization in e⁺e⁻ annihilation processes is key to probing the dynamics of particle production and decay.

Purpose of the Study:

• To report the first observation of Σ⁺ and Σ⁻ spin polarization in e⁺e⁻ → J/ψ[ψ(3686)] → Σ⁺Σ⁻ decays.
• To measure the relative phases of the form factors and decay asymmetry parameters for Σ⁺ and Σ⁻.
• To determine the CP asymmetry for Σ⁻ decays and test CP conservation.

Main Methods:

• Analysis of 1310.6×10⁶ J/ψ and 448.1×10⁶ ψ(3686) events collected by the BESIII experiment.
• Measurement of spin polarization and angular distributions in the specified decay channels.
• Simultaneous extraction of decay asymmetry parameters and CP asymmetry.

Main Results:

• Observed Σ⁺ and Σ⁻ spin polarization for the first time in these decays.
• Measured relative phases of form factors ΔΦ as (-15.5±0.7±0.5)° for J/ψ and (21.7±4.0±0.8)° for ψ(3686).
• Determined decay asymmetry parameters α₀ and α⁻₀, with α⁻₀ measured for the first time. Extracted CP asymmetry A<0xE1><0xB5><0xA_>,Σ = -0.004±0.037±0.010.

Conclusions:

• The nonzero ΔΦ values enable direct and simultaneous measurement of decay asymmetry parameters.
• The measured CP asymmetry A<0xE1><0xB5><0xA_>,Σ is consistent with CP conservation.
• This study contributes significantly to the understanding of hyperon decays and fundamental symmetries.